Association between pharmacological tenofovir adherence measures and subsequent 24-week viral load outcomes for people with HIV in South Africa.

BACKGROUND: Objective measures of antiretroviral therapy (ART) adherence, such as tenofovir (TFV) concentrations, may allow for targeted interventions to prevent future HIV viraemia. We evaluated three TFV adherence measures and their association with current and 24-week viral load (VL) outcomes. METHODS: In a South Africa-based trial, we measured urine TFV using a point-of-care (POC) antibody-based assay and two metrics assessed via liquid-chromatography-mass-spectrometry: quantitative urine TFV and TFV-diphosphate (TFV-DP) concentrations in dried blood spots (DBS). Logistic regression assessed the association between current and subsequent 24-week VL outcomes and these three measures. We also compared the baseline characteristics of individuals with detectable vs. undetectable POC urine TFV results at enrolment. RESULTS: Of 124 participants, 54.8% female, median age 39 years, 100 (81.5%) had detectable POC urine TFV and 23 (18.5%) did not. Higher TFV-DP concentrations in DBS were negatively associated with viraemia at 24-weeks (OR 0.83, 95% CI 0.725-0.928, p=0.003), whilst a detectable POC urine TFV (OR 0.62, 95% CI 0.22-1.82, p=0.380) and quantitative urine TFV (OR 0.98, 95% CI 0.95-1.00, p=0.153) showed no significant association. Compared to those with detectable POC urine TFV, those with undetectable POC urine TFV were more likely to be viraemic at enrolment (78.3% vs 25.7%, p<0.001) and have a CD4 count <200 cells/uL (34.8% vs 12.9%, p=0.001). CONCLUSION: DBS TFV-DP was associated with viraemia at 24-weeks and could help predict future viraemia. Undetectable POC urine TFV was associated with recent ART initiation, current viraemia, and lower CD4 count.